Why is my code faster with append() in a loop than with a large list?
python at mrabarnett.plus.com
Mon Jul 6 13:20:59 EDT 2009
Dave Angel wrote:
> MRAB wrote:
>> <div class="moz-text-flowed" style="font-family: -moz-fixed">Dave
>> Angel wrote:
>>> It would probably save some time to not bother storing the zeroes in
>>> the list at all. And it should help if you were to step through a
>>> list of primes, rather than trying every possible int. Or at least
>>> constrain yourself to odd numbers (after the initial case of 2).
>> Or stop looking for more factors when you've passed the square root of
>> num. I don't know what effect there'll be on the time if you recalculate
>> the square root when num changes (expensive calculation vs smaller
>> search space).
> But if I remember the code, it stopped when the quotient is one, which
> is usually sooner than the square root. And no need to precalculate the
> square root.
If the number is a large prime then the code will try all the numbers up
to that, eg if num == 1000003 then it'll try 2..1000003 even though it
could've given up after 1000.
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